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News Article | April 26, 2017
Site: www.nature.com

The consequences of a magnitude-7.8 earthquake that struck New Zealand on 14 November 2016 are still rippling through the country. The quake, which killed two people and caused billions of dollars of damage, ruptured a complex set of geological faults near the surface. It also triggered slow-motion movement as deep as 40 kilometres in Earth’s crust, some of which continues to this day, scientists report. That deep ‘slow slip’ is worrying, because it adds to the risk of another big quake. “This earthquake is special,” says Bill Fry, a seismologist at GNS Science, a government-owned Earth-science research organization in Lower Hutt, New Zealand. He and others described their findings last week in Denver, Colorado, at a meeting of the Seismological Society of America. The November Kaikoura tremor is a rare example of a large quake triggering widespread slow slip. And what researchers have learned from this tremor could illuminate the seismic risk in other regions that experience slow slip, such as Japan and the US–Canadian Pacific Northwest. A spate of large earthquakes has rattled New Zealand in the past decade, including one in 2011 that devastated the city of Christchurch. But the Kaikoura tremor stands out for its geological complexity. It began near the north end of New Zealand’s South Island and ripped northward for more than 170 kilometres1. At least 21 separate faults broke along the way. Landslides buried roads and the shaking damaged buildings in the central business district of Wellington2. The earthquake immediately triggered slow-slip movement in at least three separate areas, according to GNS Science. The regions stretched from off the east coast of the North Island to the northern part of the South Island. In each case, the Australian and Pacific plates of Earth’s crust ground against one another extremely slowly, at a dangerous interface known as a subduction zone. Most of the slow slip ceased within weeks, although a little of it continues. Cumulatively, the plate motions have released as much energy as a magnitude-7.3 earthquake would have. These patches of Earth’s crust have slipped slowly before — but never all at once, said GNS Science seismologist Anna Kaiser at the meeting. The areas in motion surround a section that experiences no slow slip at all. This region, extending east of Wellington, may be locked and building up stress that could break in the next large quake. Seismologists have observed slow-slip movement in other subduction zones, in some cases coming before large tremors, including the devastating magnitude-9 Tohoku quake in Japan in 2011. How the two phenomena relate to one another is not entirely clear. “We’re at the very early stages of trying to understand the relationship between slow-slip events and earthquakes,” says Laura Wallace, a geophysicist at GNS Science and the University of Texas at Austin. The revelations from New Zealand could alter future planning in quake-prone areas. Earthquake forecasts look at past seismic activity and calculate the probability of tremors of a certain magnitude within a certain time period. They typically do not include the effects of slow slip. But after the Kaikoura quake, GNS scientists added that movement into their own calculations and found a 5% chance of a similar quake within a year. That is a relatively low probability, but is still six times higher than it was before the quake. With the New Zealand government busy retrofitting buildings and roads in preparation for future quakes, researchers are working to quantify what they do and do not know. For instance, seismic-risk models typically consider the rupture of one fault at a time — but after Kaikoura, geologists now realize they need to plan for the possibility of the simultaneous rupture of multiple faults. “This just really emphasizes that that needs to be done,” says Matt Gerstenberger, a GNS seismologist who works on the national seismic-hazard model. Researchers will gain greater insight into slow-slip movement late this year and next, when several project teams descend on the region. In November, the JOIDES Resolution ship will begin the first of two expeditions to drill into the slow-slip area off the New Zealand coast. A ship-borne seismic survey, to begin in early 2018, will provide a 3D look at where the slow slip is happening. And a bevy of new ocean-bottom seismometers will track the shaking as the plates continue to move. “It will be the best-imaged slow-slip area, anywhere in the world,” Wallace says. “We’re trying to apply everything we can to this.”

New Zealand was struck with a 7.8 magnitude earthquake in November 2016. Now, scientists said that the Kaikoura quake, as the event is known, is the most complex recorded. Their findings could also mean higher risks of large earthquakes happening elsewhere and these include the so-called Big One in California. Seismologists had long assumed that individual faults and isolated segments of longer faults rupture independent of each other. The idea places a cap on the size of potential earthquakes fault zones can generate Findings of a new study of the New Zealand earthquake, one of the largest that hit the island in modern history, however, now put this long-held idea into question. Study researcher Ian Hamling, from the GNS Science in New Zealand and colleagues found that the heavy shaking in the earthquake that occurred just after midnight on Nov. 14, 2016 was due to ruptures of at least 12 different faults. The quake was so strong it was powerful enough to cause seabed to lift out of the water exposing seaweed-covered rocks and marine animals above tide levels. Some of the faults are so far apart. The faults in one case were separated by more than 15 kilometers (9.3 miles). Separate faults such as these were believed to be immune to the influence of other faults. Hamling said that the long-held idea was that gaps between faults of around 5 kilometers (3.1 miles) stop a rupture from continuing. The findings suggest that scientists may have been misjudging seismic hazards with the idea that slips on isolated faults may not add up to something bigger. The New Zealand earthquake was far larger that it would have been if it did not jump the gaps. The Kaikoura earthquake ruptured in stages across separate faults, which led to more shaking. Scientists think that previously unknown connecting faults could be behind this and the faults involved in the earthquake may join up lower in the ground. The phenomenon increases the maximum size of a potential earthquake. It also changes the likelihood of bigger earthquakes such as the feared Big One happening. The Big One is the hypothetical earthquake with magnitude 8 or greater expected to happen along California's San Andreas Fault. More faults acting together provide more ways to assemble big earthquakes which increases their likelihood. "This complex earthquake defies many conventional assumptions about the degree to which earthquake ruptures are controlled by fault segmentation, and should motivate re-thinking of these issues in seismic hazard models," researchers wrote in their study, which was published in the journal Science on March 23. Given the possibility of several individual faults rupturing simultaneously, the estimated chances of a magnitude 8 or larger earthquake occurring in California in the next three decades increased from 4.7 percent to 7 percent . The chances of smaller earthquakes happening over this period, however, dropped by about 30 percent. "I think it's a wake-up call," said seismologist Ned Field, from the U.S. Geological Survey in Golden, Colorado. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.

Davies T.,University of Canterbury | Davies T.,Durham University | Beaven S.,University of Canterbury | Conradson D.,University of Canterbury | And 10 more authors.
International Journal of Disaster Risk Reduction | Year: 2015

Quantitative risk assessment and risk management processes are critically examined in the context of their applicability to the statistically infrequent and sometimes unforeseen events that trigger major disasters. While of value when applied at regional or larger scales by governments and insurance companies, these processes do not provide a rational basis for reducing the impacts of major disasters at the local (community) level because in any given locality disaster events occur too infrequently for their future occurrence in a realistic timeframe to be accurately predicted by statistics. Given that regional and national strategies for disaster reduction cannot be effective without effective local disaster reduction measures, this is a significant problem. Instead, we suggest that communities, local government officials, civil society organisations and scientists could usefully form teams to co-develop local hazard event and effects scenarios, around which the teams can then develop realistic long-term plans for building local resilience. These plans may also be of value in reducing the impacts of other disasters, and are likely to have the additional benefits of improving science development, relevance and uptake, and of enhancing communication between scientists and the public. © 2015 Elsevier Ltd.

Ryan M.T.,Victoria University of Wellington | Newnham R.M.,Victoria University of Wellington | Dunbar G.B.,Victoria University of Wellington | Vandergoes M.J.,GNS Science Ltd. | And 7 more authors.
Review of Palaeobotany and Palynology | Year: 2016

The occurrence of terrestrial palynomorphs in Quaternary marine sedimentary sequences allows for direct land-sea correlations and provides a means for transferring Marine Isotope Stage chronologies to terrestrial records that extend beyond the range of radiocarbon dating. Both of these important applications require an implicit assumption that the lag between pollen release and final deposition on the seafloor - here referred to as source-to-sink residence time - is negligible in relation to the chronological resolution of the sedimentary sequence. Most studies implicitly assume zero lag, and where studies do take palynomorph residence time into account, its magnitude is rarely quantified. In Westland, New Zealand, fluvial transport is the main source of delivery of terrestrial pollen offshore to the adjacent East Tasman Sea. We radiocarbon-dated organic matter carried and deposited by contemporary Westland rivers that drain catchments with varying degrees of disturbance. The ages obtained ranged widely from essentially modern (i.e., - 57 ± 22 cal yr BP) to 3583 ± 188 cal yr BP, suggesting that precisely constraining the residence time in this region is unlikely to be achieved. We also compared the timing of four palynomorph events characterising Westland's late Pleistocene, along with the well-dated Kawakawa/Oruanui Tephra (KOT), between marine core MD06-2991 and four terrestrial records from Westland. Critically, all palynomorph events and the KOT are chronologically indistinguishable with respect to the independently dated marine and terrestrial records, supporting the general principle of transferring the marine chronology onto the terrestrial records in this setting. In other regions, particularly those lacking the high soil production and erosion rates that characterise Westland, we suggest that similar tests of marine residence time should be conducted before assumptions of zero or negligible lag are invoked. © 2016 Elsevier B.V.

Breukers R.D.,Industrial Research Ltd. | Bartle C.M.,GNS Science Ltd | Edgar A.,Victoria University of Wellington
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2012

The fabrication of a series of novel, optically transparent, bulk plastic scintillators loaded with lithium methacrylate, and incorporating 2,5-diphenyloxazole and 5-phenyl-2-[4-(5-phenyl-1,3-oxazol-2-yl)phenyl]-1,3-oxazole fluorescent centres, is described. The attenuation length, photoluminescence, and both gamma ray and thermal neutron scintillation responses were compared over a range of lithium methacrylate concentrations. The maximum concentration corresponded to a weight percentage of lithium-6 of 0.63%. The photoluminescence shows a composite 2,5-diphenyloxazole and 5-phenyl-2-[4-(5-phenyl-1,3-oxazol-2-yl)phenyl]-1,3-oxazole broad band with vibronic features in the range 350-500. nm, and lifetimes in the range 0.9-2.7. ns. An increasing luminescence in a thermal neutron beam with increasing lithium-6 content is demonstrated. © 2012 Elsevier B.V.

Davies T.,University of Canterbury | McSaveney M.,GNS Science Ltd | Kelfoun K.,CNRS Magmas and Volcanoes Laboratory
Bulletin of Volcanology | Year: 2010

We propose a mechanical explanation for the low basal shear resistance (about 50 kPa) previously used to simulate successfully the complex, well-documented deposit morphology and lithological distribution produced by emplacement of the 25 km3 Socompa volcanic debris avalanche deposit, Chile. Stratigraphic evidence for intense basal comminution indicates the occurrence of dynamic rock fragmentation in the basal region of this large granular mass flow, and we show that such fragmentation generates a basal shear stress, retarding motion of the avalanche, that is a function of the flow thickness and intact rock strength. The topography of the Socompa deposit is realistically simulated using this fragmentation-derived resistance function. Basal fragmentation is also compatible with the evidence from the deposit that reflection of the avalanche from topography caused a secondary wave that interacted with the primary flow. © 2010 Springer-Verlag.

Procter J.N.,Massey University | Cronin S.J.,Massey University | Fuller I.C.,Massey University | Lube G.,Massey University | Manville V.,GNS Science Ltd.
Geology | Year: 2010

At 11:18 h (New Zealand time, GMT +12) on 18 March 2007 an impoundment of 0.01 × 106 m3 of tephra collapsed, releasing 1.3 × 106 m3 of water from Crater Lake at 2536 m elevation on Mount Ruapehu. The lahar traveled 200 km along the Whangaehu River. Aerial LiDAR surveys of the upper 62 km of flow path were made before and after the lahar. We present here the first large-scale quantification of the geomorphic impact of the dam-break flood along with the rates and controls on its sediment entrainment and deposition. The flood mobilized a net value of 2.5-3.1 × 106 m3 of boulders, gravel, and sand over the first 5 km of travel to form a lahar of at least 4.4 × 106 m3 passing instruments at 6.9 km. LiDAR volume-transfer calculations match dynamic measurements made. After a logarithmic increase in cumulative net sediment entrainment, the lahar appeared to reach its maximum sediment-carrying capacity at 22 km. Patterns of alternating sediment erosion and deposition occurred that dominantly reflect a combination of channel morphology and confinement on the local sediment-carrying capacity of the flow. © 2010 Geological Society of America.

Ryan M.T.,Victoria University of Wellington | Dunbar G.B.,Victoria University of Wellington | Vandergoes M.J.,GNS Science Ltd | Neil H.L.,NIWA Ltd | And 4 more authors.
Quaternary Science Reviews | Year: 2012

Paleo-vegetation records developed from marine sedimentary sequences offer considerable potential for examining changes in terrestrial climate beyond the range of 14C dating because they can be independently dated by δ 18O stratigraphy. Here we present the first pollen record of vegetation from a marine core site in the Tasman Sea, TAN0513-14 (42°18'S, 169°53'E), ~110 km west of New Zealand's South Island. An independent chronology provided by correlating the Globigerina bulloides δ 18O record at TAN0513-14 to a global isotope stack shows that the record extends back to 210 ka. Glacial to interglacial changes in palynomorph content are characterised by shrub and podocarp-broadleaf forest taxa respectively and are correlated with similar changes in the ca 150 kyr-long terrestrial pollen record from Okarito Pakihi (bog), 110 km to the south southeast. Both records are placed on the same timescale by matching variations in Dacrydium cupressinum and Fuscospora between sites, with a unique tie point provided by the ca 25.4 ka Kawakawa Tephra. Our Southern Hemisphere mid-latitude vegetation records show forest extent is greatest during periods of low ice volume, high mean annual sea surface temperature (MASST) and anti-phased with local insolation intensity. However, there are several features not attributable to changes in mean annual temperature. First, a fundamental change in forest composition occurred at Termination II (TII), with a loss of southern beech (Nothofagus) from the study area. Second, the amplitude of MASST change through MIS 5 is not reflected in corresponding changes in forest extent, suggesting other feature(s) of regional climate (seasonality, frostiness, ice cover) exert important controls over vegetation patterns at these latitudes. © 2012 Elsevier Ltd.

Davies T.R.H.,University of Canterbury | McSaveney M.J.,GNS Science Ltd | Boulton C.J.,University of Canterbury
Journal of Structural Geology | Year: 2012

As a confined static grain mass is increasingly stressed, elastic strain energy accumulates in the grains; when local stress somewhere exceeds grain strength, grain breakage radiates this stored energy to the surrounding grains as a brief high-intensity pulse of pressure energy. Local grain stresses in a stressed static fault-zone follow a known probability density distribution in which the maximum local grain stress resulting from a given applied stress increases with fault-plane area. Tectonic stress buildup on a fault increases the probability of local stresses sufficient to break grains. Brittle failure of a grain releases strain energy that can trigger cascading failure of a large fault at relatively low applied stress, culminating in fault rupture, if the fault strength distribution is sufficiently homogeneous. Such ruptures can occur at lower driving stresses in larger faults. This process correctly explains the magnitude of the failure stress of the peninsula segment of the San Andreas fault, so may significantly affect fault rupture strength. Grain fragmentation also plays a significant role in dynamic fault friction; in dense comminuting granular flows, grain fragmentation causes continuous recycling of elastic-strain energy. During cataclastic fault slip, widespread grain comminution thus generates and maintains an intense high-frequency elastic energy field that causes dynamic weakness. This process is sufficiently powerful to explain the magnitude of the dynamic slip resistance of the San Andreas fault. © 2011 Elsevier Ltd.

Daly M.,GNS Science Ltd | Johnston D.,GNS Science Ltd
Journal of Applied Volcanology | Year: 2015

The Auckland Engineering Lifelines Project (A.E.L.P.) was initiated by the Auckland Regional Council, New Zealand, in 1996 to reduce the damage to and downtime of utilities such as water, wastewater, gas, power, etc., resulting from a variety of natural and technological hazards. A key initial project was a volcanic risk assessment. This paper describes the methodology that was developed to specifically assess the volcanic risk to lifelines from the Auckland Volcanic Field and distal volcanic centres in the central North Island, the application of the risk assessment and further developments beyond the initial project. © 2015 Daly and Johnston.

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